Mycobacterium avium subspecies paratuberculosis in the etiology of Crohn’s disease, cause or epiphenomenon?

Table 1 The infective theory of inflammatory bowel disease etiology

Infectious agent	Ref.	Current position
Bacterial
Listeria monocytogenes	[6]	Dismissed
Pseudomonas maltophila	[7]	Dismissed
Mycobacterium kansasii	[8]	Dismissed
Bacterioides fragilis	[9]	Dismissed
Chlamydia pneumoniae	[10]	Dismissed
Adherent-invasive Escherichia coli	[19-22]	Active
Proteobacteria	[23]	Active
Mycobacterium avium subspecies paratuberculosis	[24-26]	Active
Viral
Measles virus	[11,12,14-18]	Dismissed
Cytomegalovirus	[13]	Dismissed

Table 2 Direct methods for dectection of Mycobacterium avium subspecies paratuberculosis

Method	Tissue analyzed	Ref.	+/-	Advantage	Defect
MAP culture				Effective isolation of microorganism	Organism’s fastidious nature; slow-growth
	Intestinal biopsy	[55]	+
	Peripheral blood	[57,59,60]	-
PCR for MAP-specific IS900 DNA				Fast and easy isolation of MAP fragment	Not able to distinguish vital MAP vs fragment of killed MAP;confounded by frequent MAP opportunistic infection (oro-fecal route)
	Intestinal biopsy	[53-55]	+
	Peripheral blood	[58]	+
	Peripheral blood	[59,60]	-
	Stools	[63]	-
PCR for MAP-specific IS900 DNA				Demonstrate the presence of active/vital metabolic processes	Difficult to reproduce (RNA half-life measured in min)
	Intestinal biopsy	[62]	+

+: Supporting Mycobacterium avium subspecies paratuberculosis (MAP) hypothesis; -: Contrasting MAP hypothesis; PCR: Polymerase chain reaction; IS900: Insertion sequence 900; DNA: Deoxyribonucleic acid; RNA: Ribonucleic acid.

Table 3 Indirect methods for detection of Mycobacterium avium subspecies paratuberculosis: humoral and cellular mediator of immune response to Mycobacterium avium subspecies paratuberculosis

Method	Tissue analyzed	Antigen/cellular mediator	Ref.
ELISA for antibody detection
	Peripheral blood	38-kDa, 24-kDa, 18-kDa	[64]
		p35 vs p36	[65]
		14-kDa, AhpC, HSP	[66]
		MAP protoplasmic antigen	[67]
		18-kDa	[68]
		Anti-PPA	[69]
		Ptp-A	[43]
		Ptp-A, protein kinase G	[46]
ELISA for cytokine detection (proliferative assay)
	Peripheral blood lymphocytes	INFγ; IL-17	[71,72]
	Gut biopsies lymphocytes T CD4+	INFγ; IL-17	[73]
	Peripheral blood monocyte THP-1	TNFα	[74]

ELISA: Enzyme-linked immunosorbent assay; AhpC: Alkyl hydroperoxide reductase C; HSP: Heat shock proteins; PPA: Ptp-A protein tyrosine phosphatase; INF-γ: Interferon-gamma; IL-7: Interleukin 7; TNFα: Tumor necrosis factor alpha.